A number of techniques have been proposed for improving the access time for Internet resources, from the user's point of view. Prefetching strategies, for example, attempt to load documents into a client before the user has actually selected any of these documents-for browsing. When a user selects a hyperlink in a currently viewed document, or identifies a document using a uniform resource locator (“URL”), the addressed document may have already been prefetched and stored on or near the user's machine, thus reducing the document access time observed by the user.
Most commercial client-side online Web prefetching agents, such as those commercially available from International Microcomputer Software, Inc. (IMSI) of San Rafael, Calif., employ a greedy prefetching strategy. Greedy prefetching strategies allow the user to specify some prefetching parameters, such as the amount and kind of resources to be prefetched and the minimum user idle time before initiating prefetching, and then prefetch as many embedded hyperlinks as possible in a Web page that is currently displayed in a browser. Prefetching continues until the user requests a new Web page using the browser or when all hyperlinks and their embedded documents or hyperlinks have been prefetched.
Non-greedy client-side online Web prefetching agents, such as user history-based prefetching strategies, try to anticipate the embedded hyperlinks the user is likely to select. User history-based prefetching strategies make decisions according to prior observed user behavior. The observations may be Web page-specific and applied when a user revisits the same Web page, such as in how many cases the user clicked on a particular embedded hyperlink in a given Web page, or browser-specific, such as by (i) content category, (ii) geography of the server, or (iii) the distribution of hyperlink clicks in different portions of Web pages, for example, where the user is attracted to advertising. For a more detailed discussion of user history-based prefetching strategies, see, for example, Carlos R. Cunha and Carlos F. B. Jaccoud, “Determining WWW User's Next Access and Its Application to Prefetching,” Second IEEE Symp. on Computers and Communications (1997), incorporated by reference herein.
Such greedy and user history-based prefetching strategies frequently prefetch Web pages that can be obtained relatively quickly from their respective origin servers anyway. If a Web page can be obtained quickly, prefetching the Web page will lead to only minor access speed improvements, while potentially incurring high network and server overheads as well as unnecessary local resource consumption because the user might never access the prefetched page. User history-based prefetching strategies-attempt to minimize unnecessary prefetching by prefetching only Web pages that are likely to be accessed by the user. However, if the user selects to follow a hyperlink that the prefetching strategy did not anticipate, the user will experience the same access speed as without a prefetching agent. Moreover, the probability of a user history-based strategy selecting a Web page that the user will actually access can be very low when the user browses a large variety of different Web pages or exhibits an otherwise inconsistent browsing behavior.